1. Field of the Invention
The present invention relates to a metallic fastening member such as a tee nut or a rivet having a flange portion extending outwards from one end of a hollow shaft portion, and a fabrication method of such a metallic fastening member. More particularly, the present invention relates to a metallic fastening member including a relatively thin-walled portion to be caulked at an end of a shaft portion opposite to the end of a flange portion, and a fabrication method of such a metallic fastening member.
2. Description of the Background Art
A conventional tee nut having a thin-walled portion to be caulked at its shaft portion is disclosed in, for example, U.S. Pat. No. 5,238,344 or U.S. Pat. No. 5,348,432.
A tee nut 11 defined in U.S. Pat. No. 5,238,344 has a configuration as shown in FIGS. 40A and 40B. The tee nut is formed integrally by sheet metal processing an iron metal plate, and includes a shaft portion 12 and a flange portion 13 extending or extruding outwards from a first end of shaft portion 12.
Shaft portion 12 has a hollow cylindrical shape of uniform outer diameter. At a second end of shaft portion 12 opposite to the first end, a portion to be caulked 14 is provided. In shaft portion 12 excluding portion 14 to be caulked, a female thread 15a is formed at the inner circumference of a female thread formation portion 15. Portion 14 is made thinner than female thread formation portion 15. This provides the advantage that, in the formation of female thread 15a, the threading work can be effected from either side of the first end or the second end of shaft portion 12.
Flange portion 13 includes two pawls 16 formed by extruding or deforming inwards a portion of the outer rim of flange portion 13 so as to protrude towards the second end of shaft portion 12. The two pawls 16 are arranged opposite to each other by 180 degrees. At the rim of flange portion 13, a notch 17 having a cross section of substantially a semicircle is left as a result of formation of pawl 16.
FIG. 42A shows tee nut 11 in its usage state. Referring to FIG. 42A, shaft portion 12 is inserted into a through hole 18 that is provided in a workpiece, i.e. object of fixation 19, formed of resin or wood. Portion 14 is subjected to a caulking process by a caulking device, whereby a caulk portion 14a is formed at one surface side of object 19 of fixation. At the same time, pawl 16 digs into the other surface side of object 19. Thus, fixation of tee nut 11 to object 19 is completed.
A tee nut 31 disclosed in U.S. Pat. No. 5,348,432 has a configuration as shown in FIGS. 41A and 41B. Similar to the above-described tee nut 11, tee nut 31 is integrally formed by applying a sheet metal process on an iron type metal sheet. Tee nut 31 includes a shaft portion 32 and a flange portion 33 extruding outwards from one end of shaft portion 32. Shaft portion 32 includes a female thread formation portion 35 having a female thread 36 formed at the inner circumference of shaft portion 32. Shaft portion 32 further includes a portion 34 to be caulked. The structure of tee nut 31 differs from tee nut 11 in that two pairs of pawls 37 and 38, and 39 and 40 extending from one end towards the second end are arranged opposite each other in the radial direction of flange portion 33 at the outer perimeter of flange portion 33. Flange portion 33 substantially has an octagonal shape as a whole.
Such a tee nut 31 is generally referred to as a "hopper feed tee nut". This is because tee nut 31 can be advanced smoothly along the supply track in a nut fixation device to be fastened to a workpiece or object of fixation. In other words, the tee nut can be supplied automatically. Details of a form of a hopper feed tee nut are disclosed in, for example, G. B. Patent No. 1,157,734.
In FIG. 41B, the aforementioned supply track 43 is depicted in phantom lines. Supply track 43 includes a pair of guide rails 44 and 45 having a C-shaped cross section, arranged symmetrically facing each other. Tee nut 31 is moved taking a predetermined posture along supply track 43 while flange portion 33 is received in each of guide rails 44 and 45 with pawls 37-40 therebetween. Although not depicted, supply track 43 is often bent to set tee nut 1 at a desired posture, and has shaft portion 32 aligned in a hole formed in the workpiece object to be fastened (not shown).
As shown in FIG. 42B, for example, tee nut 31 is used in a manner similar to that of tee nut 11. More specifically, shaft portion 32 of tee nut 31 is inserted into a through hole 18 in an object of fixation 19. A caulking process is applied on portion 34 to be caulked of tee nut 31 by a caulking device, whereby a caulk portion 34a is formed at one side surface of object 19. At the same time, pawls 37-40 dig into the other side surface of object 19.
Tee nut 31 is prevented from being detached from through hole 18 by means of pawls 37-46 that prevent rotation of tee nut 31 with respect to object 19 and by means of flange portion 33 and caulk portion 34a that sandwich object 19 therebetween. Tee nut 31 is firmly secured to object 19. The fixed state is maintained substantially permanently.
Once either of the conventional tee nuts 11 and 31 is secured to object 19 by means of caulking, it is difficult to detach the tee nut from object 19 since the fixation strength is extremely great. This is preferable from the standpoint of holding the product to which tee nut 11 or 31 is applied in a secure state.
However, when the product is no longer used and is to be dismantled to recover the material forming object 19 for recycling purposes, tee nut 11 or 31 must be unfastened from object 19. The application of recycling is particularly required in the event that the material forming object 19 is a resin. There is a demand for a tee nut that does not bar the separation and recovery work of an object 19 for recycling in a product that was fastened by caulking and is now to be dismantled.
Such a demand for facilitating the separation work for recycle usage is not limited to a tee nut. There is a similar demand for any metal fastening member that is fixed by caulking to an object of fixation such as a rivet which is a member that does not have a female thread formed at the inner peripheral surface of the shaft portion.